1. Field of the Invention
This invention relates to a method for exchanging at least one secret initial value between a processing station and a chip card, in an initializing step for the chip card.
2. Description of Related Art
Such methods have been known for some time and are used in producing chip cards, which are employed today in many areas, e.g. in access control systems or as means of payment, for the purpose of safe operation of the chip cards. The chip card usually comprises an integrated circuit and coupling elements electrically connected with the integrated circuit and used for communication with external devices, for example a processing station. The coupling elements are designed either in the form of contact surfaces for touch contacting or as coils for non-touch contacting.
In conventional methods the last step performed in producing the chip card is initialization and personalization of the chip card. This provides the software pre-conditions for loading all data required for later operation of the card into the memory of the integrated circuit. During initialization all globally necessary data are transmitted for this purpose and the necessary file structures set up. During personalization the individual data are transmitted from the processing station to the chip card and stored in corresponding memory spaces. The data needed for personalization can be for example the name, address and a secret key.
To ensure that the personalizing data, in particular for example a secret key, cannot be intercepted during personalization to avoid later misuse, initialization and personalization are in the known method usually performed in separate process steps and sometimes also in separate rooms with different personnel. During initialization a serial number stored on the chip card is for example transmitted for this purpose to the processing station. For transmission the processing station has a terminal. Furthermore the processing station usually has a security module to which the terminal passes on the number of the chip card. In the security module a key is generated with the number of the chip card, the key being transmitted to the chip card by means of the terminal.
In the following personalizing step, data from a data base containing the data necessary for personalization are transmitted to the chip card and stored in the corresponding memory spaces of the chip card. The personalizing data of the personalizing data base are usually present in encrypted form. In order to avoid misuse, the key for decrypting the personalizing data is normally not known to the manufacturer of the chip card. This key is known only to the institute making the personalizing data available, for example a bank issuing the chip card to be used as a means of payment. For further processing of the encrypted personalizing data, they are loaded into the security module of the processing station. The security module offers a separate unit which is specially protected against attempts at manipulation. The security module contains the key needed for decrypting the personalizing data. With this key the personalizing data are decrypted in the security module and then encrypted again with the key generated during initialization, which was previously loaded into the chip card from the security module. The thus encrypted data are transmitted to the chip card from the security module via the terminal. Subsequently the encrypted data are decrypted with the known key in the chip card and stored in the corresponding memory spaces of the integrated circuit of the chip card.
The known method thus has the disadvantage that at least at one time, namely during initialization of the chip card, a secret key needed for data transmission between a processing station and a chip card must be transmitted once in plaintext. If this key is intercepted, all data and secret keys transmitted in the later personalizing step can be decrypted. If the key is individual to a card, at least the security of this one card would be broken.